Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as an energy source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, medium- or large-sized devices, such as vehicles, use a medium- or large-sized battery module having a plurality of battery cells electrically connected with each other because high output and large capacity are necessary for the medium- or large-sized devices.
The battery module is a battery structure in which a plurality of unit cells are electrically connected in series and/or in parallel with each other. It is very important for the battery module to maintain the arrangement structure of the unit cells such that the unit cells can be sequentially connected with each other.
Especially, cylindrical secondary batteries, which are used as the unit cells of the battery module, have great difficulty in maintaining the arrangement structure due to the appearance characteristics thereof. For this reason, the use of additional fixing members is necessary for the cylindrical secondary batteries. For example, there has normally been used a method of arranging cylindrical secondary batteries and fixing the arranged cylindrical secondary batteries with fixing tape or coating the arranged cylindrical secondary batteries with plastic so as to maintain the arrangement structure of the cylindrical secondary batteries. According to circumstances, double-sided adhesive tape may be attached between the unit cells so as to further increase the coupling force between the unit cells.
However, the strength of the fixing tape and the plastic coating is small, and therefore, the possibility is very high that the fixing tape and the plastic coating are damaged or broken. Consequently, the fixing tape and the plastic coating are not suitable for stably maintaining the arrangement structure of the unit cells. In addition, when the battery module is constructed using the fixing tape or the double-sided adhesive tape, a process for detaching and attaching the fixing tape or the double-sided adhesive tape is complicated and troublesome, which is a factor that increases the time necessary for constructing the battery module.
Generally, it is possible for the battery module to have various outputs and capacities by adjusting the number of the unit cells connected with each other. For the cylindrical unit cells, however, a fixing member for maintaining the arrangement structure of the cylindrical unit cells is requisite. Consequently, there is a problem that various kinds of fixing members must be manufactured depending upon the number of unit cells to be assembled when the battery module is constructed with the cylindrical unit cells.
In this connection, Japanese Unexamined Patent Publication No. 2000-100401, Japanese Patent Registration No. 3679705, Japanese Unexamined Patent Publication No. 1995-85896, Japanese Unexamined Patent Publication No. 2004-31284, Korean Patent Registration No. 497252, and Korean Unexamined Patent Publication No. 2005-384 disclose a member used to mount two cylindrical batteries. However, these conventional mounting members have several problems in that it is not possible to secure the stable mounting of the cylindrical batteries due to the structural characteristics of the mounting members, and additional members are necessary to connect a plurality of mounting members, as required, when a battery module is prepared.
For example, Japanese Unexamined Patent Publication No. 2000-100401 discloses a structure in which a passageway is formed through opposite sides of a spacer at predetermined regions of the spacer excluding opposite ends of the spacer so as to prevent the deterioration of the charge and discharge characteristics due to the accumulation of heat generated when charging and discharging a battery module including cylindrical secondary batteries tightly attached to each other. With this structure, however, a plurality of spacers must be coupled with each other by welding, by bonding, or by additional coupling members, when the plurality of spacers are used to manufacture a battery module, with the result that the manufacturing process is complicated, and therefore, the production efficiency is lowered. Furthermore, when the spacers are coupled with each other, for example, by spot welding, as disclosed in the above-mentioned conventional arts, the welded parts and the terminal parts of the batteries may be brought into contact with each other due to external impact with the result that external short circuits may occur. When the battery module constructed using the spacers is mounted in a vehicle, the batteries of the battery module may explode or catch fire during the use of the battery module. Consequently, the disclosed spacers seriously affect the safety of the battery module.